Field of the Invention
The present invention relates to a lighting device, a lighting system, and an external power source device, and particularly relates to a technique for discriminating a type (a classification, a model) of an external power source device that is connected to the lighting device.
Description of the Related Art
An electronic flash device as a lighting device that is built in an image pickup apparatus or that is detachably mounted on an image pickup apparatus is generally provided with a light emitting component, such as a xenon tube, and a main capacitor for supplying electric power to the light emitting component. For example, Japanese Laid-Open Patent Publication (Kokai) No. 2001-215576 (JP 2001-215576A) and Japanese Laid-Open Patent Publication (Kokai) No. 2003-098577 (JP 2003-098577A) disclose electronic flash devices each of which is provided with a booster circuit for boosting battery voltage to high voltage in order to supply electric power to a main capacitor. JP 2001-215576A discloses a technique that controls the booster circuit that charges the main capacitor according to a comparison result of capacity of a battery in an external power source device and capacity of a battery in the electronic flash device when the external power source device for the electronic flash (hereinafter referred to as an “external power source device”) is connected. JP 2003-098577A discloses a technique that controls the booster circuit that charges the main capacitor according to a comparison result of a consumption state of a battery in an external power source device and a consumption state of a battery in the electronic flash device when the external power source device is connected.
A conventional electronic flash device to which an external power source device is connectable is generally provided with three terminals including a high voltage input terminal for supplying electric power to a main capacitor, an SEH-signal terminal for controlling and determining an external power source device, and a GND terminal. However, the conventional electronic flash device is not provided with a means for discriminating an old-type external power source device and a new-type external power source device that is improved in predetermined electrical performance. Accordingly, when the external power source devices of different types are electrically connectable to the electronic flash device, there is a problem that the electronic flash device cannot exert the function of the connected external power source device sufficiently even if the new-type external power source device that is improved in the electrical performance is connected.
In order to solve such a problem, there is a method to add a detection signal line for discriminating the type of the connected external power source device to the electronic flash device. However, since it is necessary to provide a terminal corresponding to the detection signal line in this case, the number of terminals changes, which loses the physical compatibility of a connector that consists of a plurality of terminals. Accordingly, there is a problem that only one of the old-type external power source device and the new-type external power source device that is improved in the electrical performance is allowed to connect.